Determining properties of subsurface earth formation is a critical element in maximizing the profitability of oil and gas exploration and production. In order to improve oil, gas, and water exploration, drilling, and production operations, it is necessary to gather as much information as possible on the properties of the underground formation formations as well as the environment in which drilling takes place. Thus, well logging typically produces a large amount of information that needs to be analyzed to provide insights into the geological formation properties. The data to be analyzed are typically derived from logging operations using different instruments to probe various geophysical properties. Each of these instrument may generate an enormous amount of data, rendering the analysis difficult. In addition, it is often necessary to compare and contrast data from different measurements to gain insights into the formation properties.
For example, neutron tools are often used to provide information on formation porosity because formation liquids in pores interact with neutrons. However, because both water and hydrocarbons produce signals in neutron measurements, neutron logging data by themselves cannot reveal which pores contain water and which contain hydrocarbons. On the other hand, resistivity tools can easily differentiate whether a formation liquid is water or hydrocarbons, due to the high contrast in resistivity/conductivity in these two types of fluids. A combined use of these two measurements can provide information as to which formation pores contain hydrocarbons. In order to derive useful information from various formation logging data, it is a common practice to present each measurement data set in a strip chart graph (“track”) and align various graphs side by side for analysis.
For example, FIG. 1 shows a typical prior art methods of presenting a plurality of logging data as side-by-side tracks for analysis. The presentation shown in FIG. 1 is a standard format prescribed in, for example, Standard Practice 31A, published by the American Petroleum Institute, Washington, D.C. In this example, tracks 50, 54, 56 each include a header 57 which indicates the data type(s) for which a data curve or curves 51, 53, 55, 59 are presented in each track. Well log data are typically recorded with reference to the depth of well. A depth track 52, which shows the measured depth (MD, the depth from the top of the well along the borehole) of the data, is typically included in the graph as shown in FIG. 1 to provide a representation of the well.
A presentation such as shown in FIG. 1 may include in the various curves 51, 53, 55, 59 “raw” data, such as detected voltages, detector counts, etc. actually recorded by well log instrument, or more commonly, a parameter of interest that is derived from the raw data, such as gamma density, neutron porosity, resistivity, acoustic travel time, etc.
The data tracks presented in a conventional graph (e.g., curves 51, 53, 55, 59 in tracks 50, 54, 56 of FIG. 1) have several drawbacks. First of all, the conventional graphs were designed to present two dimensional well log data. Such graphs were sufficient for displaying well logging data obtained using the traditional well logging tools with sensors to measure two dimensional data only. Modem well logging tools, however, often include an array of sensors installed on the outer surface of the tool. At any particular depth, the sensors on the tool can measure formation properties in several directions around the surface of the borehole. While the tool travels through the borehole, well logging data are continuously recorded against the MD. Thus well logging data obtained using modem well logging tools are three dimensional and not two dimensional. To present such three dimensional well logging data on a two dimensional graph would require manipulation of the date, such as taking an average of the data at different MD, or take a two dimensional “slice.” Both methods fail to present the three dimensional data in the form they existed, and there have been attempts to represent formation property data in three dimensions. One such attempt is the three dimensional visualization method disclosed by U.S. Pat. No. 6,862,530, and shown in FIG. 2. According the '530 patent, the borehole trajectory is accurately depicted with respect to its MD, true vertical depth (TVD, the depth measured vertically from the ground surface), azimuth and deviation. Formation property data graphs are attached on (or exposed by) to the borehole surface. It is possible to display two separate sets of graphs of formation data using two cylinders, one cylinder in solid color and the second cylinder translucent. However, because both cylinders are plotted on the same surface, it is difficult to see both cylinders at the same time. For example, it is hard to see the second cylinder clearly if its color is too light. On the other hand, making the second cylinder darker will prevent one from seeing the first cylinder clearly.
Another drawback of the system disclosed by the '530 patent is that the method is primarily designed to display formation information of or adjacent to the borehole. For example, radius is a property of the borehole while conductivity is a property of the formation adjacent to the bore hole. Both data are suitable for displaying using the method of the '530 patent. To display such information, one needs to plot the information “wrapped around” the borehole as shown by FIG. 2. A reservoir engineer, however, often desires to understand “deep” formation information, which is the formation information away from the borehole. This is because data obtained on or adjacent to the borehole are often not a true indication of the formation property due to damages caused during the drilling process, such as damages caused by drilling fluid pressure and chemicals. In order to determine formation information away from the borehole, modern logging tools are designed to measure formation information a far distance away from the borehole. For example, with modern well logging tools measurement made at a location 90 ft away from the borehole is possible. It is foreseeable that in the near future well logging tools would allow the investigation of formation information at even farther distances away from the well borehole. Currently well logging tools with capability of determining deep formation information include tri-axial induction, crosswell electromagnetic imaging, borehole seismic and acoustic imaging, compressional radial difference, etc and tools under the Schlumberger Technology Corporation's service names of MSIP (Sonic Scanner), MRX (MR Scanner), FMI, OBMI, and Decision Express, etc. The method of '530 patent was not designed for displaying this type of data.
In a closely related technical field, there are also efforts to present three dimensional seismic data on a two dimensional plane as shown in FIG. 3. There is no well borehole involved, as normally seismic information is obtained without drilling a well. There are three known methods to displaying the data at locations that do not fall on the surface of the cube. The first way is to slice the cube so that the point of interest is exposed. The second way is to make the cube translucent and hope to see the point of interest. The third way is to use a complex virtual reality system and figuratively walk into the cube to the point of interest. A variation of the seismic cube, using two simultaneous slices through the cube, is shown in FIG. 4. This technology is not suitable for presentation of well logging data because, rather than analyzing data at one specific point, a user of well logging data is more often interested in looking at the change of certain data along a certain dimension, such as the azimuth or the MD. Seismic cube does not allow such comparison easily.